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Questions and Answers
What is the cellular arrangement of Staphylococci?
What is the cellular arrangement of Staphylococci?
Which of the following is a coagulase positive Staphylococcus?
Which of the following is a coagulase positive Staphylococcus?
What enzyme does Staphylococcus aureus produce that is significant for clot formation?
What enzyme does Staphylococcus aureus produce that is significant for clot formation?
Which of the following is NOT a characteristic of Staphylococcus aureus?
Which of the following is NOT a characteristic of Staphylococcus aureus?
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What is the significance of teichoic acid found in Staphylococcus aureus?
What is the significance of teichoic acid found in Staphylococcus aureus?
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How is Staphylococcus aureus primarily transmitted?
How is Staphylococcus aureus primarily transmitted?
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What distinguishes Methicillin-resistant Staphylococcus aureus (MRSA) strains?
What distinguishes Methicillin-resistant Staphylococcus aureus (MRSA) strains?
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Which virulence factor is associated with causing wound infections by Staphylococcus aureus?
Which virulence factor is associated with causing wound infections by Staphylococcus aureus?
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What is the primary cause of Scalded Skin Syndrome caused by Staphylococcus aureus?
What is the primary cause of Scalded Skin Syndrome caused by Staphylococcus aureus?
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Which of the following symptoms is NOT typical of septic shock?
Which of the following symptoms is NOT typical of septic shock?
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What characterizes the systemic infections caused by Staphylococcus aureus?
What characterizes the systemic infections caused by Staphylococcus aureus?
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Which toxin is specifically associated with food poisoning due to Staphylococcus aureus?
Which toxin is specifically associated with food poisoning due to Staphylococcus aureus?
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Which of the following infections is NOT caused by Staphylococcus aureus?
Which of the following infections is NOT caused by Staphylococcus aureus?
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What is a major consequence of the cytokine production induced by Enterotoxin B?
What is a major consequence of the cytokine production induced by Enterotoxin B?
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Which of the following conditions is associated with high fever and subsequent circulatory collapse?
Which of the following conditions is associated with high fever and subsequent circulatory collapse?
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Which of the following is a characteristic of non-pyogenic skin infections caused by Staphylococcus aureus?
Which of the following is a characteristic of non-pyogenic skin infections caused by Staphylococcus aureus?
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What is a primary clinical concern associated with Staphylococcus epidermidis?
What is a primary clinical concern associated with Staphylococcus epidermidis?
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Which characteristic is NOT true for streptococci?
Which characteristic is NOT true for streptococci?
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Which group of streptococci produces a clear zone around their colonies on blood agar?
Which group of streptococci produces a clear zone around their colonies on blood agar?
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What type of infections is Staphylococcus saprophyticus primarily known for causing?
What type of infections is Staphylococcus saprophyticus primarily known for causing?
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What is the primary pathogen among the Streptococci species?
What is the primary pathogen among the Streptococci species?
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What is the method of classification for beta-hemolytic streptococci that is based on carbohydrate antigens?
What is the method of classification for beta-hemolytic streptococci that is based on carbohydrate antigens?
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Which condition is often associated with Streptococcus pyogenes due to the production of erythrogenic toxin?
Which condition is often associated with Streptococcus pyogenes due to the production of erythrogenic toxin?
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Which characteristic differentiates gamma-hemolytic streptococci from alpha and beta types?
Which characteristic differentiates gamma-hemolytic streptococci from alpha and beta types?
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What inflammation is primarily caused by Streptococcus pyogenes, especially among children?
What inflammation is primarily caused by Streptococcus pyogenes, especially among children?
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Which bacterium is a major cause of sepsis in neonates?
Which bacterium is a major cause of sepsis in neonates?
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What role does Streptokinase play in medical treatment?
What role does Streptokinase play in medical treatment?
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What is the primary mechanism of hemolysis for beta-hemolytic streptococci?
What is the primary mechanism of hemolysis for beta-hemolytic streptococci?
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What is a characteristic feature of necrotizing fasciitis caused by certain strains of Streptococcus pyogenes?
What is a characteristic feature of necrotizing fasciitis caused by certain strains of Streptococcus pyogenes?
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Which of the following is a common inhabitant of the human microbiota that can cause infections?
Which of the following is a common inhabitant of the human microbiota that can cause infections?
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What disease can arise from a throat infection with Streptococcus pyogenes?
What disease can arise from a throat infection with Streptococcus pyogenes?
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What is the mode of transmission for Streptococcus pyogenes?
What is the mode of transmission for Streptococcus pyogenes?
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What severe condition may result from the rapid spread of Streptococcus pyogenes in the body?
What severe condition may result from the rapid spread of Streptococcus pyogenes in the body?
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What is the primary cause of Puerperal Sepsis?
What is the primary cause of Puerperal Sepsis?
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Which of the following complications is characterized by damage to heart valves due to autoimmune responses?
Which of the following complications is characterized by damage to heart valves due to autoimmune responses?
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Which organism is associated with nephritogenic strains responsible for Acute Glomerulonephritis?
Which organism is associated with nephritogenic strains responsible for Acute Glomerulonephritis?
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What treatment or intervention is most critical for managing the complications sequential to a Streptococcal infection?
What treatment or intervention is most critical for managing the complications sequential to a Streptococcal infection?
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What symptom is NOT commonly associated with Acute Glomerulonephritis?
What symptom is NOT commonly associated with Acute Glomerulonephritis?
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What type of antibodies are formed due to cross-reacting human antigens after Streptococcus pyogenes infection?
What type of antibodies are formed due to cross-reacting human antigens after Streptococcus pyogenes infection?
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How long after a streptococcal infection can Acute Glomerulonephritis develop?
How long after a streptococcal infection can Acute Glomerulonephritis develop?
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Study Notes
Gram-Positive Cocci
- Gram-positive cocci are spherical bacteria arranged in characteristic patterns
- Gram-positive cocci can be divided into staphylococci and streptococci
- Staphylococci form grape-like clusters while streptococci form chains
Staphylococci
- General features: spherical, Gram-positive, arranged in grape-like clusters, catalase-positive, non-motile, facultative anaerobic bacteria
- Medically important species include Staphylococcus aureus (most important), Staphylococcus epidermidis and Staphylococcus saprophyticus
- Classification based on coagulase enzyme: coagulase-positive (produce coagulase) and coagulase negative (do not produce coagulase)
- Staphylococcus aureus is the example of coagulase-positive
- Staphylococcus epidermidis and Staphylococcus saprophyticus are examples of coagulase-negative species
- Coagulase: enzyme inducing plasma coagulation by activating prothrombin to thrombin and then fibrin
- important virulence factors: Teichoic acid, Collagen-binding proteins (in attachment), and different exotoxins (proteases like collagenase and elastase, lipases, hyaluronidase, Pore-forming toxins like PV Leukocidin, Toxic Shock Syndrome Toxin (TSST), Exfoliative toxin(scalded skin syndrome) , Enterotoxin B)
Staphylococcal Infections
- Local skin infections (tissue destruction and pus formation): folliculitis, boils, wound infections, furuncles, carbuncles
- Systemic infections (reach the blood stream): septicemia, endocarditis, osteomyelitis, meningitis, pneumonia, septic shock
- Septic shock can be caused by Teichoic acid or TSST.
Staphylococcus aureus
- Epidemiology/Transmission: 30-50% of people carry in anterior nares, 5% in vaginas, spreading possible via hands, skin, throat and other surfaces
- MRSA (Methicillin Resistant Staphylococcus aureus) common, VRSA appeared
- important virulence factors: Teichoic acid, Collagen-binding proteins, Exotoxins and Exfoliative Toxin: involved in scalded skin syndrome and causes tissue damage, and Enterotoxin B involved in food poisoning.
Other diseases caused by S. aureus
- Non-pyogenic skin conditions: cellulitis and impetigo
- Scalded skin syndrome(SST): epidermolytic toxins (exfoliative toxins) cleave desmogleins in superficial skin layers causing massive skin exfoliation; fever, large areas of skin slough, secondary infections, electrolyte imbalances can occur
Staphylococcal Food Poisoning
- Ingestion of food heavily contaminated with S. aureus strains containing enterotoxin B can result in self-limiting vomiting and watery diarrhea.
- Enterotoxin B: a super-antigen that induces cytokine production in mesenteric lymph nodes after food ingestion
- Cytokines stimulate vomiting center in the brain
Staphylococcus epidermidis and Staphylococcus saprophyticus
- Both coagulase-negative staphylococci
- S. epidermidis is part of the normal human skin flora (90% of normal skin microbiota) found on skin and mucous membranes
- It commonly infects intravenous catheters and prosthetic implants (e.g. prosthetic heart valves, vascular grafts, prosthetic joints (arthritis or osteomyelitis)
- It can cause sepsis in neonates and peritonitis in patients with renal failure on peritoneal dialysis
- S. saprophyticus causes urinary tract infections, especially in sexually active young women
Streptococcus
- Spherical, Gram-positive cocci that form chains
- Catalase-negative
- Are non-motile
- Facultative anaerobes
- Classified based on hemolytic activity: Alpha-hemolytic, Beta-hemolytic, Gamma-hemolytic
- Alpha-hemolytic: green zone around colonies due to hemoglobin reduction to methemoglobin
- Beta-hemolytic: clear zone around colonies due to complete lysis of red blood cells
- Gamma-hemolytic: no change around colonies
- Classification based on Lancefield Grouping: important CHO antigen of the cell wall (e.g. C carbohydrate)
Streptococcus pyogenes (Beta-hemolytic/Group A)
- Key pathogen
- Commonly found in skin and throat
- Important virulence factors: M protein (anti-phagocytic), capsule (anti-phagocytic, surface disguise), Teichoic acid(can cause toxic shock), Pore-forming toxins (hemolysins like Streptolysin), Pyogenic exotoxin A, (super-antigen, causing toxic shock)
- Infections: Pharyngitis (strep throat), scarlet fever (rash, strawberry tongue), Otitis media, bronchitits, pneumonia (bacteremia, septic shock), meningitis, non-pyogenic skin infections (cellulitis and impetigo), toxic shock (systemic disease), Streptococcal gangrene (necrotizing fasciitis), Erysipelas, Puerperal sepsis (childbirth fever)
- Post-Streptococcal diseases: Acute glomerulonephritis, acute rheumatic fever (immune reaction against streptococcal M protein), subcutaneous nodules, Sydenham’s chorea
Post-Streptococcal diseases
- Acute glomerulonephritis: inflammatory condition affecting glomeruli (kidneys) due to cross-reacting antibodies binding to human antigens
- Acute rheumatic fever: inflammation of heart valves caused by immune response to streptococcal M protein and other antigens causing heart valve damage
Other Streptococcus
- Viridans streptococci: commonly found in the oropharynx
- Streptococcus agalactiae: found in vagina and colon
- Enterococci and anaerobic streptococci: found in the colon
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Description
This quiz explores the characteristics and classifications of Gram-positive cocci, focusing on staphylococci and streptococci. It discusses the unique arrangements, medically important species, and the significance of coagulase in bacterial classification. Test your knowledge about these essential microorganisms in microbiology.
